1. Field of the Invention
This invention relates to gas turbine apparatus having a gas turbine and a plurality of burners which burn fuel in combustion air to supply combustion gases to drive the gas turbine. The invention is particularly concerned with the control of the burners, particularly the fuel-air ratio of the burner or of an individual stage of the burner, and thus also provides methods of control or operation of a gas turbine having a plurality of burners.
2. Description of Prior Art
Large power output gas turbines are nowadays usually supplied with combustion gas by a plurality of burners, which are often arranged in a ring, with each burner supplying its combustion gas to a different part of the first stage of the turbine. A number of proposals for control of the burners in such an apparatus have been made in the prior art, and include methods of pre-setting the burners for operation, and also adjusting the burners collectively or even separately during operation. Such methods are generally concerned with control of the fuel-air ratio.
One arrangement for setting the fuel-air ratio of a pre-mixing combustion stage of a plurality of burners is described in JP-A-61-195214. A pre-mixing combustion stage is one in which the fuel and combustion air meet and pass along a passage in which they are pre-mixed before reaching a combustion zone. This device is illustrated in FIGS. 7 to 9 of the accompanying drawings.
FIG. 8 show the burners 3 arranged in a ring to supply combustion gases to one gas turbine 1, whose inlet stage 1a is seen in FIG. 7. Each burner 3 as shown in FIG. 8 includes a diffusion combustion chamber 7a in which diffusion combustion having high combustion stability is effected, and a pre-mixing combustion chamber 6a in which pre-mixing combustion having a high NO.sub.x reduction ratio is effected. However, in the pre-mixing combustion, the combustion stability range is relatively narrow.
Diffusion fuel nozzles 9 for injecting a primary fuel F1 into the diffusion combustion chamber 7a are disposed at the upstream end of the diffusion combustion chamber 7a. Air A1 for the diffusion combustion enters through openings 7b. A pre-mixing gas formation chamber or passage 23 for pre-mixing a secondary fuel F2 and air A2, with pre-mixing fuel nozzles 19 for injecting the secondary fuel F2, is disposed at the up-stream end of the pre-mixing combustion chamber 6a. A movable member 28 of an inter-flow control device (hereinafter referred to as "IFC") is disposed near the inlet of the pre-mixing chamber 23 in order to regulate the rate of the combustion air flowing into the chamber 23 from the space between a burner casing 18 and a transition piece 105 and between the burner casing 18 and a cylinder 6 bounding the pre-mixing combustion region 6a. The air is supplied into this space as a flow A from a compressor 1.
The IFC device comprises the movable member 28, an IFC opening setter 29a for determining the amount of opening of the movable piece 28 and an IFC driving mechanism 17a for driving the movable member 28. One IFC opening setter 29a is provided for the plurality of burners 3. As shown in FIGS. 8 and 9, the IFC driving mechanism 17a comprises a control ring 45 disposed around the outside of the annular ring of burners 3, a hydraulic cylinder 46 for rotating this control ring 45 and a lever link mechanism 47 for driving the movable member 28 of each burner 3 in accordance with the operation of the control ring 45. The movable member 28 of the IFC device and the lever link mechanism 47 are provided for each of the burners 3, but other parts are in common for all the burners 3. In FIGS. 8 and 9, the arrows indicate the movement of the parts in the opening (O) and closing (C) directions.
As another means for adjusting the air distribution inside the burner, it is known to provide a bypass valve 104 for passing part of combustion air, supplied from the compressor to the gap between the gas turbine casing 18 and the transition piece 105, directly into the transition piece 105 as shown in FIG. 10. In the same way as in FIGS. 7 to 9 described above, only one bypass valve opening setter 100a, one motor and one control ring 102, etc, constituting the bypass valve driving device 100a are provided, to control all the bypass valves 104 of all the burners 3a, respectively. A link mechanism 103 for driving the bypass valve 104 in accordance with the operation of the control ring 102 is arranged for each bypass valve 104.
As for control of the fuel-air ratio (the proportion of the fuel to air) in such a gas turbine equipment, the fuel-air ratio has been set to a constant value by changing the flow rate of air in accordance with the flow rate of the fuel that is predetermined for the operation of the gas turbine as described in JP-A-60-66020 for example. In this case, the air flow rate is determined only on the basis of the fuel flow rate which is in match with the gas turbine load. Determination of the air flow rate based on only the fuel flow rate has been practised in other gas turbine equipments.
In such conventional gas turbines one control ring 45, 102 is driven for a plurality of burners. Therefore, the control of the fuel-air ratio for each burner individually cannot be made.
A proposal for the separate control of each burner has been made in JP-A-59-7739, which shows fuel control for each burner performed, on the basis of the sensed temperature at the inlet to the first stage of the gas turbine. Each burner is controlled in dependence on the temperature pattern sensed all around the turbine, so as to minimize the temperature differences measured around the gas turbine, resulting from different performance of the burners, by means of feed back from the sensed temperatures. Overall improvement of the performance of the gas turbine, particularly in respect of a reduction of nitrogen oxide content in the exhaust gas and of stability of the burner operation, was not under consideration. This method also does not control each burner in dependence on a performance characteristic thereof.
In U.S. patent application Ser. No. 5,024,055, there is described a device for gas turbine control in which sensors are provided at the outlet of the turbine, to detect the presence of unburned gas components in the exhaust gas. Such unburned components suggest that one or more of the burners is operating incorrectly or has blown out, and from the angular position of such unburned components, is possible to determine which burner is in such a condition. The proposal then is to adjust the flow rate of air and/or of fuel to the respective burner, in order to maintain the fuel flow rate above a certain minimum and the air flow rate below a certain maximum.
A proposal for separate control of two rings of burners on the basis of detected fuel calorific value has been made in EP-A-278699.